1. Field of the Invention
The present invention relates to a wireless communication system, a wireless communication apparatus and a wireless communication method, and a computer program by which a plurality of wireless stations intercommunicate with each other within a LAN such as a wireless LAN (Local Area Network). More particularly, the present invention relates to a wireless communication system, a wireless communication apparatus and a wireless communication method, and a computer program by which a wireless network is operated by each communication station communicating in an autonomous, distributed manner.
Further more particularly, the present invention relates to a wireless communication system, a wireless communication apparatus and a wireless communication method, and a computer program by which isochronous data such as AV content is transmitted efficiently under an autonomous, distributed wireless communication environment. Even more particularly, the invention relates to a wireless communication system, a wireless communication apparatus and a wireless communication method, and a computer program by which band-guaranteed data transmission is implemented under an autonomous, distributed wireless communication environment.
2. Description of Related Art
Among universal wireless network standards are IEEE (The Institute of Electrical and Electronics Engineers) 802.11 (e.g., see Non-Patent Document 1), HiperLAN/2 (e.g., see Non-Patent Document 2 or 3), IEEE 302.15.3, Bluetooth communication, and the like.
Generally, in order to construct a own area network using wireless technology, a method is employed by which an apparatus serving as a control station called an “access point” or a “coordinator” is provided within an area to form a network under an overall control by this control station.
In a wireless network having such access point, in a case where a communication apparatus transmits information, the following access control method is widely adopted. That is, the communication apparatus reserves a band necessary for its transmission at the access point so that the transmission does not collide with that of another communication apparatus. That is, by providing the access point, synchronous wireless communication is implemented in which communication apparatus within the wireless network synchronize with each other.
However, in a wireless communication system where an access point is present, in a case where asynchronous communication is to be implemented between a transmitting side and a receiving side, it is necessary to implement a wireless communication via the access point, and this imposes a problem that utilization efficiency of the transmission line is halved.
On the other hand, as another method of constructing a wireless network, “ad hoc communication” has been devised in which terminals directly intercommunicate to each other a synchronously. For a small-scale wireless network involving a relatively small number of adjacent clients, among others, ad hoc communication is considered appropriate in which arbitrary terminals can directly intercommunicate asynchronously without using a specific access point.
Since no central control station is present, an ad hoc wireless communication system is suitable for constructing, e.g., a home network composed of home appliances. The ad hoc network, as the routing is automatically changed in the event that one of the terminals breaks down or has its power turned off, is provided with features that the network is hard to fail, and that data can be transmitted to relatively remote locations at high data rates by causing packets to hop a plurality of times between mobile stations. Many examples of ad hoc networking developments are known (e.g., see Non-Patent Document 4).
For example, in an IEEE 802.11 wireless LAN system, networking under IEEE 802.11 is based on the concept of BSS (Basic Service Set). BSS includes two types, one of which is a BSS defined by an “infra mode” in which a master station such as an AP (Access Point, or control station) exists, and an IBSS (Independent BSS) defined by an “ad hoc mode” that is composed only of a plurality of mobile terminals (mobile stations). In the latter, ad hoc mode, terminals operate on a Peer-to-Peer basis in an autonomous, distributed manner without providing a control station. And when a beacon transmission time arrives, each terminal counts a random period, and unless it receives a beacon from any other terminal until the period expires, it transmits a beacon.
On the other hand, in order to transmit data having isochronism, and continuity in terms of time, such as AV content whose data needs to be sent periodically at fixed intervals, a band must be guaranteed. For example, the IEEE 802.11 TG-e is studying a communication method under the premise of band guaranteed communication using a wireless LAN.
However, in implementing band-guaranteed communication in a conventional wireless LAN system, it is commonplace to use a technique by which a specific control station is designated so that the control station manages communication resources on a centralized basis and thus assigns time for use that becomes available in a limited way within a particular group. Thus, the resulting configuration is such that the power of transmission is given to a communication apparatus serving as a sender of information on a centralized basis, and a wireless communication apparatus as a reception destination is controlled by the sender communication apparatus as being subject thereto.
In this case, this configuration is premised on the fact that a communication apparatus serving as a specific control station is designated, and thus it is not applicable to any system in which no control station apparatus is provided. Particularly, if an ad hoc network is formed without providing a specific control station to implement band-reserved communication, it is difficult to determine to what extent considerations should be given to its influence. Further, since the power of transmission is given to a communication apparatus serving as a sender of information on a centralized basis, a wireless communication apparatus serving as a reception destination cannot send a notice that it is using a band for receiving a signal at a predetermined timing.
Furthermore, in order to transmit data having isochronism, i.e., continuity in terms of time, isochronous communication is performed. In this case, a predetermined communication band (or time) for implementing isochronous communication is secured beforehand, and in the communication band (or time), communication is implemented exclusively between specific communication apparatuses.
For example, as technology of a wireless personal area network (WPAN) in IEEE 802.15.3 that is being under standardization at the time of filing this application, a predetermined communication band is secured as a guaranteed time slot (GTS) to implement isochronous communication within the band.
However, if it is intended to perform a band guaranteed communication such as an isochronous communication in a conventional wireless LAN system, a scheme must be used to share band-guaranteed traffic with other communication apparatus. Thus, a specific control station must be designated, and the control station apparatus must manage communication traffic on a centralized basis. In other words, in a wireless communication system in which a specific control station is not provided, such band-guaranteed communication cannot be applied directly.
Further, at a time of isochronous communication, communication between other communication apparatus must be eliminated, and thus, even in this sense, the control station must specify a communication apparatus that uses the time, on a centralized basis. That is, it is extremely difficult to realize band-reserving communication such as isochronous communication by forming an ad hoc network.
Furthermore, even if communication which is totally free from any interference at both ends of the network is established in by centralized management performed with a specific control station, if the control station allocates different bands for different communications, a problem arises therefrom that throughput is reduced.    Non-Patent Document 1: International Standard ISO/IEC 8802-11: 1999 (E) ANSI/IEEE Std 802.11, 1999 Edition, Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications    Non-Patent Document 2: ETSI Standard ETSI TS 101 761-1 V1.3.1 Broadband Wireless Access Networks (BRAN); HYPERLAN Type 2; Data Link Control (DLC) Layer; Part 1: Basic Data Transport Functions    Non-Patent Document 3: ETSI TS 101 761-2V1.3.1 Broadband Wireless Access Networks (BRAN); HIPERLAN Type 2; Data Link Control (DLC) Layer; Part 2: Wireless Link Control (RLC) sublayer    Non-Patent Document 4: C. K. Tho, “Ad Hoc Mobile Wireless Network” (published by Prentice Hall, PTR)